This invention relates to hydrolyzing nitriles with water to produce their corresponding amides, and catalysts useful therefore. More specifically, this invention relates to the hydrolyzing of nitriles such as acrylonitrile, preferably in aqueous solution, in the presence of a catalyst comprising metallic copper and having an optimum surface film coverage of ionic copper, to produce corresponding amides such as acrylamide.
The formation of amides by hydrolyzing nitriles with water in the presence of copper ions was taught by Greene et al. in U.S. Pat. No. Re. 28,525. The effective copper species were disclosed as being catalytic combinations of at least two selected from Cu.degree. and/or Cu(I) and/or Cu(II).
U.S. Pat. No. 3,631,104, to Habermann et al. discloses catalysts of copper, copper oxides, copper-chromium oxide, copper-molybdenum oxide or mixtures thereof for the hydration of nitriles and water to their corresponding amides. Habermann et al. teach that it is desirable to reduce the cupric oxide to cuprous oxide and that in preferred catalysts, the copper content is essentially cuprous oxide containing a minor amount of copper metal. The conversion of acrylonitrile to acrylamide in the examples generally decreased with time when cupreous catalysts alone were used. U.S. Pat. No. 3,767,706 to Habermann et al. discloses the catalyst consisting essentially of copper metal which is effective in the hydration of nitriles and water to their corresponding amides. U.S. Pat. No. 3,994,973 to Habermann et al. discloses catalysts consisting of copper prepared by reducing copper oxides, of reduced oxides, or unreduced copper oxides for use in the same process.
U.S. Pat. No. 3,994,609, Fetchin et al. discloses catalysts consisting of reduced copper-iron compounds containing from 0.2% up to about 5% iron. The conversion of acrylonitrile to acrylamide is shown to decrease with respect to the amount of time the catalyst is stored. U.S. Pat. Nos. s3,920,740; 4,000,195 and 4,014,820 to Svarz et al. disclose copper-aluminum alloy catalysts pretreated with alkali metal hydroxides, useful for hydrolyzing acrylonitrile to acrylamide.
U.S. Pat. No. 3,755,100 to Epple discloses the use of copper electrodes to electrolyze aqueous solutions of acrylonitrile with A.C. current to produce acrylamide. Epple teaches that the pH of the aqueous solution must be alkaline, adjusted to about 9.5-14. U.S. Pat. No. 3,764,494 to Allain et al. discloses the use of copper electrodes to electrolyze aqueous solutions of acrylonitrile with D.C. current to produce acrylamide. Allain et al. teach that the pH of the aqueous solution is critical and that it should be in the range of 7-10.5. A D.C. voltage of 10 V at 5 amp. was applied to the cell, reversing polarity every 5 seconds. Yield of acrylonitrile from acrylamide was about 37%.
U.S. Pat. No. 3,645,913 to Habermann discloses the regeneration of copper-containing catalysts by oxidizing the spent catalyst with an oxygen-containing gas at an elevated temperature and thereafter reducing the catalyst. U.S. Pat. No. 3,766,088 to Yashimura et al. discloses the regeneration of metallic copper catalysts by treating the spent catalyst with an aqueous solution of sodium compounds, potassium compounds, calcium compounds or ammonium compounds and thereafter washing the catalyst fully with water. U.S. Pat. No. 3,869,511 to Johnson et al. discloses maintaining or improving catalytic activity of copper catalysts defective in hydrolyzing nitriles to amides by introducing anions such as Cl.sup.-, Br.sup.-, NO.sub.2.sup.-, NO.sub.3.sup.- into the reactant feedstream. Cations such as alkali metal and alkaline earth metal ions, including sodium, are taught to be inert with respect to any improvement of catalytic activity, and anions such as acetate are taught to be either inert or to have detrimental affect on catalytic activity.
The use of various copper-containing catalysts, either consisting essentially of one of or comprising a combination of Cu.degree., Cu(I) and Cu(II), for hydrolyzing nitriles to amides therefore is known to the art. However, the optimum relations between the amounts of each copper species for the hydrolysis process has heretofore been unknown. Because the optimum formulation of the catalyst was unknown and because the copper-containing catalyst generally suffers quick deactivation, it has been necessary to wait for conversion of the nitrile to amide to fall off to begin regeneration procedures.
We have discovered that maximum catalytic efficiency in the copper-catalyzed nitrile hydrolysis process unexpectedly occurs when the copper catalyst utilized comprises elemental or metallic copper having upon its surface a film of an average of about 0.75 to about 12.5 monolayers of ionic copper.
In practicing the nitrile hydrolysis process, it is not possible to maintain peak catalyst activity for long periods of time. Unavoidable admission of air or other oxidants, including non-oxygen containing oxidants, to the catalyst due to impurities in the liquid feed, or from mechanical leaks, thickens the surface film and so causes deterioration in catalyst performance. Conversely, deterioration in catalyst performance can also result from loss of ionic copper from the surface, such as by solubilization in the reaction mixture. Simultaneous operation of both processes would tend to prolong catalyst life if rates of the two processes were similar. The two rates are evidently not similar, since significant decay of catalyst activity soon occurs.